1. Field of the Invention
This invention relates to a novel resin composition to be suitably used for sealing liquid crystal displays of a variety of types developed in recent years and to be reliably operated in severe environments. It also relates to a film-made liquid crystal cell realized by using such a resin composition.
In recent years, liquid crystal displays have become markedly popular in response to the rapid development of down-sized personal computers, audio equipment, instruments, color television sets and other electronic appliances. A liquid crystal display consumes less energy and requires less drive force than a cathode ray tube (CRT) so that it enables reductions of size, weight and cost, while producing clear and sharp images better than a CRT even in the sunlight. Because of these advantages, the scope of application of liquid crystal display (hereinafter referred to as LCD) has been constantly expanding. Particularly, tremendous efforts have been made to develop LCDs comprising a film substrate that are thin and lightweight and not damaged even if carried in a pocket of a jacket. As known glass-made LCDs, film-made LCDs are required to have outstanding physical properties. For instance, the components of the cell of the LCD need to be firmly bonded together to provide an enhanced degree of hermeticity. Therefore, they must be physically and chemically stable and resistant against moisture and heat.
2. Description of the Prior Art
Currently, a cell comprising glass substrates and liquid crystal is prepared typically by bonding upper and lower substrates by means of a one-liquid hot-cure type epoxy adhesive, injecting liquid crystal in a highly vacuum condition and sealing the remaining hole by means of a UV (ultraviolet)-light-cure type or two-liquid cold-cure type resin. Improved and highly efficient one-liquid hot-cure type adhesives are currently available and, therefore, there are practically no technological troubles for bonding glass substrates.
On the other hand, one-liquid hot-cure type or two-liquid type epoxy adhesive are used for bonding film substrates. However, a one-liquid hot-cure type epoxy adhesive is originally designed to bond glass substrates and, once cured, it becomes so hard that it is scarcely capable of withstanding bending force and adapting itself to thermal deformations of the bonded substrates and it is rather poorly adherent to the substrates. A two-liquid type epoxy adhesive is disadvantageous in that it has a relatively short pot life and does not have satisfactory physical and chemical stability to the moisture and the heat of the prepared cell. Sealing materials containing flexible epoxy resin as a principal ingredient such as a polyol type epoxy resin or a urethane type epoxy resin, have been studied, although such materials are not particularly adherent to film and, to some extent, lack physical and chemical stability to the moisture and the heat of the cells prepared by using such materials. Thus, no satisfactory adhesive has been developed so far for film substrates.
A number of adhesives have been proposed for sealing film-made liquid crystal cells, including one using thermoplastic resin varnish for dissolving the surface of substrates and bonding them by applying heat and pressure thereto (Japanese Patent Application Laid-open No. Shou 57-23669), one using a double bonding technique, where substrates are bonded together by means of a silicone resin type substance on the inside and an epoxy resin type substance on the outside (Japanese Patent Application Laid-open No. Shou 60-69634) and one that cures with heat and light (Japanese Patent Application Laid-open No. Hei 1-129232). None of these, however, has been found commercially feasible.